The medical endoscope has been used more and more widely as an important part of minimally invasive surgery. With the gradual development of minimally invasive surgery technology, a higher technical requirement has been put forward, for instance, a more promising application is currently to add the near-infrared fluorescence analysis technology in the minimally invasive procedure. This requires that the endoscope system must be equipped with a wide spectral imaging ability, must yield imaging simultaneously in the visible (400 nm-700 nm) and near-infrared (700 nm-900 nm) lights and must ensure the focal imaging in the visible and near-infrared lights. At present, the traditional endoscope system can yield imaging in the visible and near infrared lights, however, there is an off-focal distance 0.3 mm-0.5 mm between the near infrared imaging location and the visible light imaging location, which results in refocusing at the observation of the infrared fluorescence image. Refocusing will affect the doctor's operational efficiency each time as the doctor must repeatedly switch the visible light images and near-infrared fluorescent images during the surgery procedure. Therefore, there must be an endoscope system that yields the visible and near infrared images to meet the operational requirements for doctors during surgery procedures.
The endoscopic imaging system consists essentially of an endoscope optical system, a camera adapter optical system and an image sensor. The endoscope optical system consists of a main endoscope optical system and an eyepiece optical system. The main endoscope optical system is composed by an objective lens set and a steering set. The imaging quality of the endoscope is determined by the imaging quality of the main optical system. The objective lens set images the operational field into the focal plane of the objective lens set. The steering set is composed by a HOPKINS rod lens system with an odd array of amplification rate by −1 time. The steering set is designed to transfer the images yielded by the objective lens set to the final image plane of the steering set in 1:1 to ensure the adequate working length of the endoscope. The images yielded in the operational field by the main endoscope optical system becomes the virtual images after the eyepiece optical system. The camera adapter optical system projects the virtual images onto the image sensors. The images in the operational fields are sent to the monitor via circuits and software for doctor's observation.
To achieve parfocality, the entire endoscope imaging system must focus in various components under the visible and near-infrared lights. Specifically, the main endoscope optical system, the eyepiece optical system and the camera adapter optical system must be parfocal. The parfocality is judged by the defocus amount. Pertinent to this application, the defocus amount in the near infrared and visible lights can be defined as: the axial distance between the imaging location of central view field at near Infrared 850 nm wavelength and the imaging location of the central view field at the visible light 550 nm wavelength is an 850 nm defocus amount of the central view field. To simplify the description, the after-said defocus amount refers to the defocus amount of the central view field between the near infrared 850 nm and visible light 550 nm. The analysis finds that the eyepiece optical system and the camera adapter optical system have the defocus amount less than 0.02 mm when the main endoscope optical system achieves the defocus amount less than 0.05 mm and the edge view field curvature less than 0.1 mm; and the entire endoscope system can achieve the parfocal imaging when the main endoscope optical system achieves the defocus amount less than 0.02 mm and the edge view field curvature less than 0.02 mm.
It is easy to achieve the defocus amount less than 0.02 mm and edge view field curvature less than 0.02 mm in the eyepiece optical system and the camera adapter optical system, however, it is very difficult to achieve is to achieve the defocus amount less than 0.05 mm and edge view field curvature less than 0.1 mm in the main endoscope optical system. Concurrently, no literature has reported to meet the requirements.